Getting levels of the SharePoint Heirarchy and their Exceptions

Something that I have to do time and again is get some element of SharePoint’s heirarchy, such as a site collection, site, list or item. This is pretty typical – that’s why we all use USING to ensure proper disposal of SPSites and SPWebs, right? But what happens if the thing you’re after isn’t there? What exception get’s thrown? Well, this should be pretty clear: